The present invention relates to a fresh-water generating apparatus for purifying, inter alia, seawater, sludge water, oily water, and industrial waste water.
In the past, systems of heating and evaporating seawater and then cooling the water to obtain fresh water have been common as methods for purifying, inter alia, seawater, and multi-stage flushing systems have been used in which the water is distilled under reduced pressure in order to improve heating efficiency, and a large number of depressurizing chambers are combined in a practical plant (Patent Document 1). The salt concentration of the generated fresh water is low at approximately less than 5 ppm, and fresh water can be generated in large quantities.
In recent years, a system has been employed in which seawater is passed under pressure through a type of filtering membrane known as a reverse-osmosis membrane (a so-called RO membrane), and the salt in the seawater is condensed and removed to strain out freshwater, for which a large plant is constructed that exceeds 10,000 tons per day. An RO membrane requires higher pressure for filtration with higher salt concentrations in the seawater or with lower desired salt concentrations in the freshwater, and various membranes of complicated structures, known as hollow fiber membranes and spiral membranes, have been proposed to withstand this pressure (Patent Document 2). A turbine pump, a plunger pump, or another high-pressure pump is used to increase pressure.